Due to the increasing energy demands, offshore oil and gas production is moving into deeper waters. For providing an efficient and secure production, processing facilities are being installed at the ocean floor. Such subsea installations may include a range of components including pumps, compressors and the like, as well as a power grid for operating the components. The power grid may, for example, include a subsea transformer, subsea switchgear and subsea variable speed drives. The components of the subsea installation are to be protected from the surrounding sea water, in which pressures of 300 bar or more may prevail (e.g., at installation depths of 3,000 m or more).
Two solutions were proposed for dealing with these high pressures. A pressure resistant enclosure may be provided. The pressure resistant enclosure has a close to atmospheric internal pressure, enabling the use of conventional electric and mechanical components. Such enclosures are to have relatively thick walls and are thus bulky and heavy, since the enclosures are to withstand the high pressure difference.
Another solution is the use of pressurized (or pressure compensated) enclosures that include a volume/pressure compensator that balances the pressure inside the enclosure to the pressure prevailing in the ambient sea water. The pressurized enclosure may be filled with a liquid, and components operated inside the pressurized enclosure are operable in such liquid under high pressures. The pressure/volume compensator compensates for variations in the volume of the liquid filling the enclosure, which may occur due to variations in outside pressure and/or temperature.
When providing a subsea power grid including several subsea electric devices, such as the above mentioned subsea transformer, subsea switchgear and the like, the devices are to be connected electrically. Solutions exist both for pressure resistant and pressure compensated enclosures. The subsea electric devices may be connected by jumper cables. At the device, a subsea connector provides an electric connection between the interior of the device and the cable. For this purpose, dry mate and wet mate connectors are known. The design of both types of connectors is a technical challenge. A wet mate connector with flushing arrangements has an even higher complexity than a dry mate connector. Both types of connectors are to withstand the high subsea pressures, yet the connectors are to remain compact, which is a particular challenge for medium and high voltage applications. For example, for high voltage and high current ratings that may be necessary for, for example, the connection between a transformer and a distribution system, a reliable design of such connectors is very difficult and costly. The connectors (e.g., wet mate connectors) may thus represent a sensitive component that may be considered a weak link in respect of reliability.